I have not posted much on this forums but I do have experience with the LM4 and problems I caused on the field.

My comment is more like a tool list and not spare parts list.
- Valve tool
This is a must have item! The magazines will leak someday.If you get the right one,you can fix your fill valve as well as your release valve. It sucks to have a magazine leak and not be able to fix it.
- AR Wrench
If you are going to remove the barrel nut, it is wise to have one. You also need this to acces your inner barrel for changing the hop-up and such. Cleaning your inner barrel is important for performance especially for OPs with dust and dirt.
- The Speed loader adapter
Comes in very handy when loading multiple magazines. Assuming your OP lets you load on the field.
- Maybe a spare bucking? Ripped bucking != good.

Lost basically told you everything, but it wouldn't hurt to get a few charging valves for the mags as they can be damaged when not charging it correctly which is hard in a stressful environment with adrenaline. I even damaged a few at home. Plus they're cheap and easily replaceable.

Bring Q Tips and clean cotton cloths or t-shirts if the OP is longer than a day to clean the gun after using. Wipe Clean the bolt carrier, the upper receiver, and the charging handle then re-lube.

Here is a great video on cleaning & maintenance from one of our forums member Akiraspeedstar.

I don't see any need for silicone grease anywhere on the LM4 and only in the gearbox of an AEG.

Light lube of silicone on the bolt carrier (like your 5.56mm version) and may be a drop inside the carrier to lube the O-ring but taking the bolt out of the carrier all the time isn't necessary for me and has a risk of losing the c-clip, etc.

It wouldn't hurt to keep a spare o-ring though. I once had a malfunction where the oring got pinched by the bolt nozzle and carrier and it got torn up. Don't know how or why, but it hasn't happened since. Still, I'd keep a spare.

I have just gotten the HFT O ring set. Can anyone tell me off the top of their head if the smaller O rings will work for the fill valve / release valve?

Just wondering if the HFT kit covers all.

I've heard people say that some of the HFT o-rings can be used for the valves but I don't know which ones and for what parts specifically. So far I've been unable to use my LM4 much because I can't afford the mags right now and I'm having a lot of double feed issues. Another suggestion you may want to look into is the EVO II hop up/maple leaf bucking, as a lot of people here have reported amazing results. So far my LM4 has only had a HFT o-ring put in it and the range is more consistent now but I think the stock bucking is what is hindering the true capability of the gun. Plus, double feeds... I was confident that my gun would have that problem but apparently it decided to prove me wrong.

I've heard people say that some of the HFT o-rings can be used for the valves but I don't know which ones and for what parts specifically. So far I've been unable to use my LM4 much because I can't afford the mags right now and I'm having a lot of double feed issues. Another suggestion you may want to look into is the EVO II hop up/maple leaf bucking, as a lot of people here have reported amazing results. So far my LM4 has only had a HFT o-ring put in it and the range is more consistent now but I think the stock bucking is what is hindering the true capability of the gun. Plus, double feeds... I was confident that my gun would have that problem but apparently it decided to prove me wrong.

I will probably just break open a mag and work on sizing O rings to it. I am hesitant b/c I thoroughly believe in the "aint broke don't f*ck with it" philosophy, so we'll just have to see.

I did just order 2 RA-Tech barrels for both my LM4's, and im so excited i found them it damn near made my nipples hard.

I will probably just break open a mag and work on sizing O rings to it. I am hesitant b/c I thoroughly believe in the "aint broke don't f*ck with it" philosophy, so we'll just have to see.

I did just order 2 RA-Tech barrels for both my LM4's, and im so excited i found them it damn near made my nipples hard.

My nipples are always hard when I'm playing with my LM4! Yeah if your mags don't leak then just leave them alone, but I'd say chances are that they will leak at some point so you'll have a chance to check it out. Usually it's not a big deal, plus the assembly of the mags is really nice so it's quite easy so long as you know what you're doing.